The present disclosure relates to a sealed solenoid construction, and more particularly, to a sealed solenoid valve in which the solenoid coil and pole piece are protected from the environment.
Solenoids are known to be useful for directly actuating valves by applying a current to the solenoid coil to induce a magnetic flux through an armature that causes the armature to move. A direct-drive solenoid valve typically actuates a rod-shaped core armature with a proximal end coupled directly to the valve head. It is also known to use a solenoid to actuate a disc-shaped armature, called a “clapper,” that can be separated from the solenoid by a small gap, such as in a non-energized state of the solenoid. In one configuration, when the solenoid is energized, the magnetic flux crosses the gap and pulls the clapper toward, and often into contact with, the solenoid. The solenoid may provide the opposite actuation (i.e., the clapper is biased into contact with the solenoid until the solenoid is energized and pushes the clapper away). Such a “clapper valve” can be favorable over other solenoid valve constructions because, for the same size solenoid, a greater magnetic flux can be supported by the clapper surface area than by a rod-shaped armature. The greater magnetic flux results in a greater actuation force. Further, a clapper armature does not need to extend into the interior of the solenoid coil, such that a stationary pole piece can be disposed within the coil (creating a solid-core solenoid) to augment the magnetic flux.
Solenoids, and in particular solenoid coils and pole pieces, can be manufactured from many different conductive and ferromagnetic materials. In a valve that needs to be very small or lightweight, it may be desirable to, for example, choose a lighter ferromagnetic material for the pole piece than the typically-used iron or soft iron. However, it is known in solenoid-operated valves to immerse the solenoid in the working fluid in order to lubricate or protect the components, to provide a path for fluid flow or armature movement, or to facilitate pressure balancing of the valve. Where the coil and/or pole piece materials are chosen for reduced weight, they may be more susceptible to corrosion by the working fluid. In particular, valves for use in some air and space applications (e.g., rocket engines and thrust boosters) may need to be compact, lightweight, and able to control the flow of corrosive gaseous or liquid media, such as hypergolic propellants like monomethyl-hydrazine (MMH) and oxidizers like nitrogen tetroxide (N2O4). It may be unfavorable to immerse the coil and pole piece(s) in corrosive working media because such a valve design may prevent the selection of materials that provide the necessary functional properties but lesser weight, because such lightweight materials may be more susceptible to corrosion.
Solenoid-driven poppet valves can be used in flow control applications where release of a gas from the valve must be controlled accurately. Such valves benefit from being “balanced,” wherein all forces acting on the poppet are substantially equal when the solenoid is non-energized, and only a small force is needed to actuate the valve, even when high pressure media is being controlled by the valve. Typically, the balanced state is closed, with a light gauge spring holding the poppet closed. A balanced poppet valve may be actuated by a solenoid, which magnetic force only has to overcome the biasing force of the spring to actuate the valve. The low force demands less power, which allows the solenoid (i.e., the coil, pole piece(s), and housing therefor) to be smaller and lighter.
Ordinary solenoid-driven balanced poppet valves are prone to leakage in high-pressure applications due to the design and materials used. Some such valves exist that overcome the leakage problem at high fluid pressures, and thus may be used in extreme environments and mission-critical applications where the valves must operate rapidly and accurately, exhibit low hysteresis, and provide bubble-tight shut-off. In air and space applications, such valves must further be designed to contribute as little weight as possible to the craft or component in which they are used, and must withstand the extreme conditions of the application, including extremely high fluid pressures (up to 10 kpsi or higher), extreme temperatures and temperature variation (from sub-zero to well above zero), material deformation due to pressure and thermal stresses, and vibrations and stresses due to high speeds of the craft. Existing designs typically either immerse the solenoid in the working media, requiring use of relatively large, heavy corrosion-resistant materials for the solenoid components, or isolate the solenoid and armature from the working media with sealing arrangements that complicate the construction of the valve, particularly when working to meet the stringent operational, weight and form factor requirements of air and space applications.